This invention relates to cryogenic coolers particularly, to a cooling tunnel system that impinges cryogenic fluids for accelerated cooling.
Food processors use both cryogenic and mechanical freezers to chill or freeze a variety of food products. Cryogenic freezers typically freeze items to cooler temperatures with rapid cycle times. Unfortunately, these cycle times are inadequate for some applications.
A traditional cryogenic tunnel freezer for cooling foods, such as warm eggs from +95xc2x0 F. (35xc2x0 C.) to +45xc2x0 F. (7xc2x0 C.), delivers performance on the order of 3,750 BTU""s/hr/sq. foot (11,829 W/m2) of active conveyor belt. In order to obtain this performance, using a prior art carbon dioxide cooler/freezer, a 1.5 horsepower (1.1 kW) fan motor is positioned every 4.5 feet (1.4 m) along the length of its tunnel. Since a usable width of conveyor, in this example, is 18 inches (46 cm) or 36 inches (91 cm) wide considering two conveyors in use, each 1.5 horsepower (1.1 kW) fan covers an area of 1,944 square inches (12,500 cm2) or 13.5 square feet (1.2 m2). Dividing 1.5 horsepower (1.1 kW) by 13.5 square feet (1.2 m2) provides a ratio of 0.1111 horsepower per square foot of conveyor (892 W/m2). Accordingly, the prior art obtains 3,750 BTU""s per hour (11,829 W/m2) of heat transfer performance per 0.1111 fan horsepower (0.08 kW). More specifically, for every one fan horsepower 0.75 (kW) in the traditional cryogenic tunnel freezer, 33,750 BTU""s per hour (9.88 kW) of heat transfer performance are achieved. Furthermore, plant space is a major concern in typical food processing plants, especially egg processing plants that have a fixed configuration due to the egg sorting and packaging equipment already installed. Typically, the above freezer specifications are inadequate to cool eggs with a limited cooler length.
The Agriculture Department and the FDA have recently published an Advanced Notice of Proposed Regulations (ANPR) for the safe handling, labeling and temperature control of table (shell) eggs. This proposed regulation is responsive to public concern for food safety with respect to Salmonella Enteritidis in processed shell eggs. The intent of this rule is to require egg processors to lower the temperature of their shell eggs to an internal temperature of 45xc2x0 F. (7xc2x0 C.) prior to shipment. Further, distributors, food service and grocery chains are now demanding even tighter temperature specifications (i.e., 41xc2x0 F. or 5xc2x0 C.)
Currently, the favored auxiliary cooling method uses cold storage rooms. Eggs cooled in this manner can take anywhere from 2xc2xd days to 14 days to reach acceptable temperatures while in their packed containers. Since the typical egg processor handles between 750,000 to 1,000,000 eggs per day, the necessary cold storage capacity at these facilities to meet the required temperature specifications is substantial.
In current state of the art cryogenic CO2 food freezer/coolers typical shell eggs (at 101xc2x0 F. or 38xc2x0 C.) would need to be exposed to cryogenic conditions for a dwell time of at least 2 minutes. Based on typical production rates in plants using commercially available egg processing equipment, such a cryogenic CO2 cooling unit would have to be a minimum of 20-25 feet (6.1-7.6 m) long to handle the production rate of each packing head. The cooler""s packing heads are typically capable of packaging 50 cases containing 30 dozen eggs per hour (1,500 dozen/Hr.). Furthermore, the cooler""s long length is necessary to ensure efficient application of the CO2 refrigeration so as to lower the egg temperature from +95xc2x0 F. (35xc2x0 C.) to the required +45xc2x0 F. (7xc2x0 C.)
However, most processing plants can""t accommodate such length of coolers in their processing lines. Further, use of a typical xe2x80x9chigh performancexe2x80x9d cryogenic freezer/cooler configuration for such an application would be unlikely to achieve the necessary heat transfer in the required length and would be cost prohibitive.
Egg cooling has been attempted in the past at two different locations within a typical egg processing plant. It has been attempted to insert a refrigerated egg cooler between the egg washer location and the candler. This proved unsuccessful because the unit needed to be at least 70 feet.(21.3 m) long to provide the necessary cooling at the normal production rates and line speeds. U.S. Pat. No. 5,694,836, to Blevins et al., entitled xe2x80x9cMODULAR LOOSE EGG COOLING, STORAGE AND TRANSPORT SYSTEM AND METHODxe2x80x9d addresses the need for cooling of loose eggs by describing a packaging system that enables cooling fluid access thereto during storage. Blevins et al. do not consider in-line processing of packaged and boxed eggs that account for a large part of the market for shell eggs sold to retailers and food service customers.
U.S. Pat. No. 5,474,794 to Anderson et al., entitled xe2x80x9cRAPID CHILLING OF SHELL EGGS USING CRYOGENIC GASESxe2x80x9d describes the advantages of cryogenic cooling at temperatures between xe2x88x9260xc2x0 F. (xe2x88x9251xc2x0 C.) to xe2x88x92120xc2x0 F. (xe2x88x9285xc2x0 C.) as a process, but does not discuss specific cryogenic freezer/cooler designs necessary for space efficiency and economic viability.
Other examples of both cryogenic and mechanical freezer designs are described in the prior art that improve various aspects of the freezer""s performance, both from throughput and efficiency standpoints. U.S. Pat. No. 3,864,931 to Guttinger, entitled xe2x80x9cPROCESS AND APPARATUS FOR FOOD FREEZINGxe2x80x9d, describes a two zone freezing approach where a first freezing zone uses a vertical upward blowing stream of mechanically refrigerated cold vapor through a perforated solid belt to create a fluidized bed effect. A second zone includes vertical jets of cold air that are directed downward through formed slots that are transverse to the food conveyor movement direction. A blower and heat exchanger provide a source of cold gas. The velocity of the cold gas is limited to prevent product from being blown around in the freezer.
Other prior art focuses on the vapor balance of cryogenic freezers/coolers to optimize freezing efficiency. The prime motivation for these designs is to limit air infiltration into the cryogenic enclosure. Room air represents an unnecessary heat load on the system and these patents are directed towards its control and elimination.
Ovadia et al. in xe2x80x9cIMPINGEMENT IN FOOD PROCESSINGxe2x80x9d, Food Technology, April 1998, Vol 52, No. 4, p. 46, describe how impingement of cooling vapors on foodstuffs provides advantages over blast freezing. In addition, Ovadia et al. indicate that impingement freezing achieves a similar effect as does blast freezing, but at higher temperatures and lower costs. See also U.S. Pat. No. 4,523,391 to Smith et al., entitled xe2x80x9cHIGH EFFICIENCY IMPINGEMENT HEATING AND COOLING APPARATUSxe2x80x9d for a plenum design used in an impingement cooler.
Accordingly, it is an object of this invention to provide an improved cooler that operates with shorter lengths and faster cooling rates.
It is another object of the invention to provide an improved egg cooler that utilizes a cryogenic fluid to accomplish the egg cooling without freezing the interior of the eggs (i.e., yolk and white) or cracking the shell.
It is a further object of the invention to provide an improved egg cooler that utilizes carbon dioxide as a cryogenic fluid in a tunnel egg cooler.
A cooling tunnel system that includes a conveyor for carrying objects through a tunnel chamber. The conveyor enables a cooling fluid to pass therethrouqh and about the objects. A plurality of slot means feeds the cooling fluid to the conveyor means. Each slot means includes at least one aperture for enabling vapor flow onto and about the objects. A plenum adjacent the plurality of slot means distributes the cooling fluid. And at least one fan in the tunnel chamber causes a flow of the cooling fluid into the plenum and through the slot means with sufficient velocity to impinge upon and cool the objects and to recirculate the cooling fluid within the tunnel chamber.